That must be a mistake,___ it?A mustn't B can't C isn't 选什么,为什么?
问题描述：
That must be a mistake,___ it?A mustn't B can't C isn't 选什么,为什么?
答
A. 吧。前面有 must 后面就要跟。
如果换个说法，
there is a mistake, 后面就要跟 Isn't it.
答
c
a mistake 是单数
首先can't排除
然后must的疑问句和否定句用的不是must 和mustn't
排除也知道应该选c
答
That must be a mistake,___ it?
A mustn't B can't C isn't
答案：C
答
C isn't
看见must了吧，be 才是个动词，因为单数，所以 isn't